Homeostasis Physiological state of the body Internal physical and chemical conditions are maintained...
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Transcript of Homeostasis Physiological state of the body Internal physical and chemical conditions are maintained...
Homeostasis • Physiological state of the body• Internal physical and chemical conditions are
maintained within a tolerable range (balance)– Internal temperature, hormone levels, pH, pressure,
concentrations of glucose and other solutes in the blood, water balance (osmoregulation)
Extracellular Fluid• Interstitial fluid – Surrounds fills the spaces
between cells and tissues– Approx 10L– Consists of water, sugars, salts,
FA, AA, coenzymes, hormones, neurotransmitters, waste products
– Regulates flow of chemicals and allows cells to function properly
• Blood plasma– Helps movement of water and
electrolytes throughout the body
– Approx 3L
Internal Environments• Changes in Extracellular
Fluid has negative effects on cellular function
• Body uses organ systems to regulate internal conditions
– Nervous system– Endocrine system – Muscular system – Integumentary system – Excretory system – Reproductive system
Nervous System (Communication) • Brain, spinal cord, peripheral nerves, sensory organs • Receives sensory data from the environment• Informs body of external conditions• Transmits signals throughout the body
Endocrine System (Communication) • Pituitary, thyroid, pancreas, adrenal (glands)• Regulates levels of hormones and other chemicals
Excretory System (Protect the Body)• Kidneys, bladder, urethra, ureters• Rids the body of waste • Maintains clean internal environment
Integumentary System (Protect the Body) • Skin, sweat glands, hair, nails• Maintains a constant body temperature
Immune System (Protect the Body) • White blood cells• Protects/fights infection
Digestive System (Acquire Energy)• Liver• Breaks down amino
acids• Detoxifies harmful
chemicals (alcohol)• Manufactures
important proteins• Stores glucose
Circulatory System (Acquire Energy)• Transports important substances, including food
molecules, oxygen, carbon dioxide, hormones throughout the body
Respiratory System (Acquire Energy)• Exchanges oxygen and
carbon dioxide between the lungs and the atmosphere.
• Oxygen is needed to release energy from food molecules
• Carbon dioxide is a waste gas
Skeletal System (Support and Move Body)• Includes bones,
ligaments, cartilage• Bones protect
organs and are points of attachment for muscles
Muscular System (Support and Move Body)• Provide movement
for the body• 3 types– Skeletal muscle –
move skeleton– Smooth muscle –
organs – Cardiac muscle –
heart
Reproductive System (Produces Next Generation)
• Includes organs that produce and transport sperm and eggs
• Enables female to give birth
Mechanisms used in Homeostasis • Respond to internal
and external conditions
• Feedback systems– Positive/Negative
• Help bring the body back into balance
• Breathing rate, heart rate, internal temperature, blood glucose levels
Negative Feedback• Reduces the output or activity of an organ or system back to its normal range • Include 3 elements1. Sensor
– tissues or organs - detects change
2. Integrator - hypothalamus – control centre – compares conditions from environment with to optimal conditions
in the body – Set points – ranges of values which need to be maintained
3. Effector – returns measured condition back to set point – response – Antagnositc effectors – produce opposite effect of change detected
Positive Feedback Mechanisms• Increases change in
environmental condition• Does not result in
homeostasis • Cause system to become
unstable• “fight or flight” response• reproduction• fever • Positive feedback
mechanisms operate within negative feedback mechanisms
• Allows body to be brought back into balance
Thermoregulation• Internal temperature
regulation• Negative feedback
mechanism• Thermoreceptors
– compare external temp with internal set point
– Found throughout integumentary system
• Trigger responses (2)– Rate of exothermic
reactions in body (metabolism)
– Rate of thermal energy exchange through surface of body
Hypothalamus• Body’s thermostat• Maintains body
temperature• Optimal body
temperature – 35⁰ - 37.8⁰
• Signals from hypothalamus make us aware of our own temperature
• Body temp rises above hypothalamus set point → blood vessels dilate/induce vasodilation/sweating → increase blood flow→ increase thermal energy loss to environment (radiation)→ sweat glands activated → body temp decreases
• Body temp falls below hypothalamus set point → vasoconstriction in skin/ skeletal muscles start shivering→ reduced blood flow→ less thermal energy lost to environment → body temp increases
Mechanism
Mechanisms of Thermal Energy Exchange• Occurs at the surface
where body comes into contact with the external environment
• Exchange of thermal energy occurs through 1 of 4 mechanisms– Conduction– Convection– Radiation– Evaporation
• All of these mechanisms act simultaneously
Thermal Energy• Conduction
– Flow of thermal energy between molecules that are in direct contact
• Convection– Transfer of thermal
energy within a fluid (liquid or gas)
• Radiation– Thermal energy is
transferred electromagnetically
• Evaporation– Absorbs thermal energy
from skin via water/sweat
Homeotherms• Animals that maintain a stable internal
temperature regardless of external conditions• Includes – Poikilotherms– Endotherms – Ectotherms
Poikilotherms• Fish, amphibians, reptiles, and most
invertebrates• Body temperature varies with and often matches
the temperature of the external environment
Endotherms • Warm blooded animals
(mammals, birds)• Homeotherms that use
internal physiological mechanisms (metabolism) to generate thermal energy and maintain body temp
• Remain fully active over a wide range of temperatures
• Need a constant supply of energy
Ectotherms • Cold blooded animals
(reptiles, amphibians, fish)• Homeotherms that use
external sources of energy to absorb thermal energy and regulate body temperature
• Temperature fluctuates with environmental temperature
• Inactive when temp are too low
• Undergo thermal acclimatization– Gradual adjustment to seasonal
temp
Torphor, Hibernation, Estivation • Adaptations to survive
extreme climates by conserving energy
• Torphor – Sleeplike state – Metabolic rate and body
temperature drop in response to daily temp (nocturnal animals, hummingbird)
• Hibernation – State of inactivity over an
extended period of time • Estivation
– Seasonal torphor – environment is hot and water is scarce
Water Balance • Extracellular fluid needs to maintain a constant
volume (~15L) of water and balance of solute within the body
• Mechanism – Osmosis
Osmosis • Water molecules move
from a high concentration to a region of lower concentration across a selectively permeable membrane
• Osmotic pressure – Results from a difference
in water concentration gradient between the two sides of the selectively permeable membrane
• Hyperosmotic• Hypoosmotic • Isoosmotic
• Hyperosmotic– Solution with higher
concentration of solute molecules than water molecules
– Water tends to move to this side
• Hypoosmotic– Solution with lower
concentration of solute molecules than water molecules
– Water tends to move from this solution
• Isoosmotic– Solution with equal solute
and water concentrations on both sides of cellular membrane
Osmotic Environments (Cell)
Osmoregulation • Process of actively
regulating the osmotic pressure of bodily fluids
• Osmole (osmol)– Contributes to osmotic
pressure of solution • Extracellular fluid =
intracellular fluid (isoosmotic)– [solute] remains the
same across cellular membrane
– [water] remains the same across cellular membrane
The Excretory System• Main functions (with the help of osmoregulation)– Concentrate wastes and expel them from the body– Regulate fluids and water within the body
• Organs included– Kidney – Adrenal gland – Ureter– Urinary bladder– Urethra
Removal of Metabolic Waste Waste Origin of Waste Organ of Excretion
Ammonia Breakdown of amino acids in the liver kidneys
Urea Conversion of ammonia in the liver kidneys, skin
Uric Acid Breakdown of purines in food and drink kidneys
Carbon Dioxide Cellular respiration (breakdown of glucose) lungs, intestines, skin
Bile Pigments Breakdown of porphyrin ring (hemoglobin) intestines
Lactic Acid Cellular respiration (breakdown of glucose) kidney
Solid Waste Breakdown of food intestine
Mechanism• Thirst
– Physiological sensation to drink water • Stimuli to Thrist
– Hypertonicity – cellular dehydration is monitored by the hypothalamus via osmoreceptors
• Mechanism – Hypothalamus sends a signal to pituaitry gland to release
ADH (anti-diuretic hormone/vasopressin)– ADH acts on collecting tubules in nephrons making them
more permeable to water– >1% of filtered water is excreted – Reabsorption of water reduces [Na⁺] – Osmoreceptors send signal to hypothalamus stopping
release of ADH
Kidneys
• Removes waste• Balances blood pH• Maintain body’s water
balance• Blood is supplied to
kidney via renal artery • Re-enters circulatory
system via renal vein
Nephrons• Functional unit of
the kidney • (1 000 000 per
kidney)• Regulate water
balance • Conduct excretion • Different sections of
the nephron have specialized functions in formation of urine and conservation of water
Urinary Bladder• Renal pelvis connects the kidney to the ureter
which fills the bladder • Holds ~300mL-400mL of urine before exiting the
urethra
Deamination • Occurs in the liver
– breakdown of protein • Removal of amino
group from amino acid• Creates ammonia NH₃
(toxic to body)• Urea Cycle
– Ammonia reacts with bicarbonate and 2 ATP molecules to form urea
– Transported to kidneys where excretion occurs via blood
Bicarbonate Buffer System (Kidneys) • Maintains pH of blood
(acid-base homeostasis) • Regulates the excretion of
H⁺ ions in the urine and reabsorption of bicarbonate into bloodstream – TOO ACIDIC – hydrogen
ions are excreted – TOO BASIC – less hydrogen
ions are excreted • CO₂ dissolved in blood
reacts with water to form carbonic acid (H₂CO₃)
Formation of Urine • Ultimate goal
– conserve water, balance salts, concentrate wastes
• Urine – hypoosmotic to surrounding body
fluids– water tends to move from urine into
the body fluids • 3 Feature of nephron interact to achieve
ultimate goal– Arrangement of loop of Henle– Difference in permeability – Concentration gradient of molecules
and ions • 3 processes interact to achieve formation
of urine– Filtration – Reabsorption – Secretion
Formation of Urine: Overall Process
Filtration • Begins at Bowman’s capsule
(selectively permeable membrane)
• Receives water, ions, glucose, AA and urea from glomerulus
• Difference of pressure allows for transfer of molecules and ions into capsule
• 1400L of blood pass through kidneys every day
• Bowman’s capsule filters ~180L from blood
• ~1.5L is excreted as urine daily
Reabsorption • Occurs as fluid from Bowman’s
capsule enters proximal convoluted tubule, Loop of Henle and distal convoluted tubule
• Water, ions and nutrients are transferred back into interstitial fluid and peritubular capillaries via passive and active transport
• Microvilli inside tubules increase surface area
• Difference in solute concentration allows water to move across the membrane and back into interstitial fluid via osmosis (aquaporins)
Secretion • Removal of waste products from the
blood and interstitial fluid and secreted into the nephron
• Include – detoxified poisons, water soluble drugs, metabolites, H⁺
• Secretion of H⁺ ions balances acidity in body
• Reabsorption of HCO₃⁻ occurs simultaneously
• Buffer system controls pH levels of blood– Increased acidity – H⁺ excreted as urine
• Urine reaches bottom of collecting ducts, flows into renal pelvis, through ureters, into urinary bladder and exits through urethra
Kidneys Regulate Blood Oxygen Levels
• Kidneys monitor blood oxygen levels (RBC’s)
• If too low – kidneys release erythropoetin (EPO) into the blood stream which stimulates the production of red blood cells
Kidney Diseases • Renal Failure • 2 types1. Acute – rapid progressive loss of
renal function– Injuries, accidents,
complications from surgery
2. Chronic – slow progressive with long
term consequences– Diabetes mellitus,
uncontrolled hypertension, polycystic kidney diseases
• Treatments– Dialysis– Kidney transplant